Overcut, a New Theory for Tip Interference in Internal Gears

Abstract

For over forty years internal gears were surrounded by obscurity occasioned by the discovery of tip interference where calculation suggested that it would not occur (1)†. The present author developed a new theory for tip interference which gave better insight in the manufacturing process. Internal gears not satisfying rule (12) will be injured by the cutter at a centre distance still too low for involute generating. This injuring phenomenon in an early stage of cutting is called overcut. The overcut has to be neutralized by an increase of the tooth spaces to such an amount that the final generating centre distance is larger than existing theories suggested. When rule (12) is satisfied, then there is no overcut and no tip interference.